Measuring a flow rate of a fluid using a flowmeter is typically accompanied by needs for detection of a property or state of the measured fluid or a state of the fluid flowing through a measuring pipe. For example, in manufacture lines where chemicals are introduced into fluid, properties of the fluid such as conductivity and permittivity are measured, in addition to the flow rate thereof. In measuring pipes where contaminant is likely to adhere to the inner surface thereof, the adhesion state is measured to determine a maintenance cycle. Thus, there is a demand for measuring a property or state of fluid or a state of the pipe where the fluid flows as well as a flow rate thereof. In addition, there is a demand for realizing these measurements using a hardware configuration that is essentially the same as a flowmeter.
In other words, there is a demand for a single meter capable of selecting measurement of a flow rate of fluid, measurement of a state of the fluid, simultaneous measurement of a flow rate and state of the fluid, as desired by a user. The demand for simultaneous measurement of a flow rate and state of fluid means that the meter should be able to measure a property or state of the fluid independently of the flow rate of the fluid.
An electromagnetic flowmeter as an exemplary flowmeter is required to measure a state of a measuring pipe, in addition to the above needs, in terms of self-checking ability of the electromagnetic flowmeter. For example, in an electromagnetic flowmeter that uses an electrode to extract potential, insulating materials adhere to the electrode that is in contact with fluid, which precludes adequate extraction of the potential from the electrode and accurate measurement of a flow rate of the fluid. In this case, if the flowmeter can determine the cause of change in signals to be a change in flow rate of fluid therein or adhesion of insulating materials thereto, without interrupting measurement of the signals, troubles related to measured values can be prevented. In an electromagnetic flowmeter, usually, a change in a magnetic field to be applied results in errors in measured values. In this case, if the flowmeter has information about magnetic field applied to fluid, the flowmeter can determine the cause of the obtained abnormal output to be a change in flow rate of fluid or a change in the magnetic field applied to the fluid, providing the electromagnetic flowmeter with a self-checking function as the flowmeter.
As described above, it is desired to fulfill the requirements for measure various parameters other than flow rate in a hardware configuration that is essentially the same with that of a flowmeter. Examples of the devices that measure various parameters other than flow rate to fulfill the requirements are discussed in Japanese Patent No. 3164684 and Japan Measuring Instruments Federation, “A to Z of Flow Rate Measurement for Instrumentation Engineers”, Kogyogijutsusha, 1995, pp. 147-148. The flowmeter devices disclosed in Japanese Patent No. 3164684 and Japan Measuring Instruments Federation, “A to Z of Flow Rate Measurement for Instrumentation Engineers”, measure a level and a conductivity using the principle of electromagnetic flowmeter. The flowmeter devices calculate a level using a ratio between the electromotive force signals obtained from electrodes when exciting coils that are located opposite to each other around a measuring pipe are simultaneously driven and the electromotive force signals obtained from electrodes when one of the exciting coils is driven. The flowmeter devices also calculate a conductivity of fluid using a ratio between electromotive force signals before and after a change of an input impedance of a preamplifier connected to electrodes. This configuration can be used to detect substance adhesion.
Unfortunately, the electromagnetic flowmeters discussed in Japanese Patent No. 3164684 and Japan Measuring Instruments Federation, “A to Z of Flow Rate Measurement for Instrumentation Engineers”, detects a property or state of fluid based on a ratio between flow rate signals, resulting in a problem that the flow rate decreasing to zero results in a larger measurement error and lower accuracy, and no property or state can be detected at a flow rate of zero. In addition, no change in magnetic field can be detected because the cause of change in measured flow rate cannot be determined whether a change in the flow rate itself or a change in magnetic field.
To address the above problems, the inventor of the present invention proposed a state detection device as illustrated in FIG. 29 (see Japanese Patent No. 2006-90794). The state detection device includes: a measuring pipe 1 through which a measured fluid flows for measurement; a pair of electrodes 2a and 2b that are disposed perpendicular to both a magnetic field applied to the measured fluid and an axis PAX of the measuring pipe 1, and mutually opposite across the measuring pipe to be in contact with the measured fluid, so as to detect an electromotive force generated by the magnetic field and the measured fluid; an exciting coil 3 that applies, to the measured fluid, a time-changing magnetic field asymmetrical to a boundary plane PLN that is perpendicular to the axis PAX in the measuring pipe, the electrodes 2a and 2b being placed on the plane PLN; a state quantifying unit that extracts a ∂A/∂t component from resultant electromotive forces that are detected by the electrodes 2a and 2b and composed of an electromotive force of a ∂A/∂t component irrelevant to a flow velocity of the fluid and an electromotive force of a v×B component resulting from the flow velocity of the fluid, extracts a variation factor relevant to a parameter (such as a property or state of the fluid or a state in the measuring pipe) from the ∂A/∂t component to quantify the parameter based on the variation factor; and a power source 9 that supplies excitation current to the exciting coil 3.
The state quantifying unit 8 includes: a signal converting unit 5 that extracts a ∂A/∂t component from resultant electromotive forces that are detected by the electrodes 2a and 2b and composed of an electromotive force of the ∂A/∂t component and an electromotive force of a v×B component, and then extracts a variation factor relevant to a parameter from the ∂A/∂t components; a state storing unit 6 that stores, in advance, a relationship between the variation factor relevant to the parameter and the parameter; and a state outputting unit 7 that outputs the parameter corresponding to the extracted variation factor based on the relationship stored in the state storing unit 6. According to the state detection device discussed in Japanese Patent Application Publication No. 2006-90794, accurate detection of a state in a measuring pipe including a fluid and a magnetic field can be achieved independently of a flow velocity of a fluid.